1. Field
Example embodiments relate to an apparatus and method for forming a thin layer on a substrate, and more particularly, to an apparatus and method for forming an epitaxial layer on a substrate in an epitaxial growth process.
2. Description of the Related Art
Modern electronic devices are becoming more highly integrated and require increased performance. Accordingly, the line width of gate electrodes and the size of the source/drain regions are becoming smaller. Unfortunately, however, it is difficult to increase the carrier mobility of the electrons in the semiconductor devices in proportion to the size reduction of the semiconductor devices due to the band gap of strained silicon, which significantly reduces the performance of the more highly integrated semiconductor devices. For example, the electrical resistance of the gate electrode and the contact resistance at the source/drain regions each tend to increase along with the increase in the degree of integration of the semiconductor devices. Thus, the electrical resistance of the gate electrode and the contact resistance at the source/drain regions have a significant effect on the amount of device integration possible.
For those reasons, impurities may be implanted into the source/drain regions by an epitaxial process to provide high layer uniformity and increased carrier mobility, thereby forming a hetero-junction thin layer, i.e., an epitaxial layer, on the source/drain regions of the substrate. For example, silicon-germanium (SiGe) layer has been widely used for the contact layer or the impurity layer at the source/drain regions because of its high dielectric constant and the high carrier mobility of silicon germanium (SiGe).
In performing the epitaxial process for forming the epitaxial layer on the source/drain regions, the layer thickness and the composition ratio of hetero elements of the epitaxial layer can be controlled in real time using x-ray diffractometry. More specifically, the layer thickness and the composition ratio of the epitaxial layer are detected using x-ray diffractometry during the epitaxial process, and the mass flow of the source gases into a process chamber may be controlled according to the detected layer thickness and composition ratio. Accordingly, the epitaxial layer may be formed on the substrate to an expected layer thickness with an expected component ratio. Since the detected component ratios and layer thicknesses have a strong linear relationship with the mass flow of the source gases, the layer characteristics of the epitaxial layer can be in-line controlled with high reliability during the epitaxial process just by feeding back the x-ray diffractometry results to a source provider and using them to control the flow of the source gases.
However, if any dopants are provided with the epitaxial process for improving layer process characteristics, the layer characteristics of the epitaxial layer may be changed by the dopants. In particular, the dopants may cause a change in the amount of the hetero elements that participate in the growth of the epitaxial layer due to the physical properties of the dopants.
For instance, during the epitaxial process for forming the SiGe layer, when boron (B) gases are provided to reduce the band gap energy, the relative amount of germanium (Ge) particles in the SiGe layer is reduced due to the diffusitivity of boron (B). Therefore, the layer thickness and the composition ratio of germanium (Ge) of the SiGe layer is dependent upon the mass flow of boron (B) gases as well as the mass flow of the source gases, and thus the predictable linearity between the mass flow of the source gases and the layer thickness and composition ratio does not exist any more.
Since the x-ray diffractometry detects the layer thickness and the composition ratio of the epitaxial layer based on crystal structures thereof, the amount of the dopants cannot be detected by the x-ray diffractometry. Accordingly, when dopants are provided in the epitaxial process, the x-ray diffractometry results are insufficient to provide an accurate in-line control of the mass flow of the source gases for forming the epitaxial layer having the desired characteristics.